Massive sea lion, fur seal hunting in the Patagonian coasts is altering Southern Atlantic Ocean ecosystems
Sea lion hunting by the Europeans at the Atlantic coasts of South America -it started in the 19th Century and continued up to the second half of the 20th century in Argentina and Uruguay- changed its nutrition guidelines of these pinnipeds as well as the structure of the coastal trophic network, according to the studies by the team codirected by Lluis Cardona, from the Department of Evolutionary Biology, Ecology and Environmental Sciences and the Biodiversity Research Institute of the University of Barcelona (IRBio), and Enrique Crespo, from the Patagonian National Center and the National University of Patagonia (Argentina).
|The current diet and ecological role of these big marine vertebrates in the south of the American continent |
are quite different from what they used to be [Credit: Massimiliano Drago, UB-IRBio]
This research is one of the results of the project Efectes de l'explotacio humana sobre depredadors apicals i l'estructura de la xarxa trofica del Mar Argenti durant els darrers 6000 anys (Effects of human exploitation on apex predators and structure of the trophic network in the Argentinian sea over the last 6000 years), financially supported by BBVA Foundation and led by Professor Alex Aguilar (UB-IRBio), head of the Research Group on Large Marine Vertebrates of the University of Barcelona.
A megafauna exploited by humans in all oceans
Hunting and fishing usually create a reduction in the abundance of bigger species. Therefore, megafauna is considered to be one of the most threatened compounds of biodiversity. Marine mammals are an essential element of megafauna in all oceans and they have been extremely exploited by humans. However, knowing about the effects of this exploitation on the functioning of food networks in marine ecosystems -a high complex structural framework- is still a hard challenge for the scientists due to the difficulty to perform manipulative experiments.
|Experts from the IRBio assess the ecological impact caused by the exploitation of marine resources at the |
southern coasts of South America over the last 6000 years [Credit: Massimiliano Drago, UB-IRBio]
Sea lions, abundant predators in South American waters
The South American sea lion (Otaria flavescens) is a marine mammal with a robust physique and a short and flatter snout, which is present in the coasts of South America, from Peru to Cape Horn and Brazilian coasts. With a similar geographical distribution, the South American fur seal (Arctocephalus australis) is half its size, with a longer snout and eats mainly pelagic fish, having a lower position in the food pyramid of the marine ecosystem compared to the other species.
|Sea lions and fur seals are now apex predators, that is, superpredators |
[Credit: Lluís Cardona, UB-IRBio]
When massive sea lion hunt affects natural habitats
Applying analytical techniques of C and D stable isotope ratios in an innovating way to sea lion and fur seal bones -from archaeological sites from both Patagonia and Tierra del Fuego- the experts could rebuild the pinnipeds diets in different time periods of the second half of the Holocene and compare them to the current ones.
|The authors applied analytical techniques of C and D stable isotope ratios to sea lion and fur seal bones |
from archaeological sites [Credit: Fabiana Sapporiti, UB-IRBio]
New superpredators in the marine ecosystem
With the arrival of the Europeans in the 16th century -and specially the phase of massive marine resources exploitation that started in the late 19th century- the diet of sea lions and fur seals changed. Human pressure eradicated both species, something which ended up altering the food pyramid and the ecological role of these marine large vertebrates at the south of the American continent, according to the authors. "Sea lions and fur seals have now a higher trophic level compared to the times of the Europeans' arrival. They are now apex predators, that is, superpredators" says Cardona.
|An archaeological site before being excavated in Tierra del Fuego |
[Credit: Lluís Cardona, UB-IRBio]
Is it possible to bring back those ecosystems altered by human action?
The effects of the marine ecosystem exploitation alter the length of the trophic network. According to the authors, if the apex predators are extinguished, the trophic network gets shorter. However, if they are only less present, the trophic network of the ecosystem can grow due the decrease in intraspecific competition.
New researchers on historical ecology in the southern regions of the American continent can shape new scenarios on the ecosystems altered by human action. "These works show that the ecological niche we now see in wild species can differ from what they had in natural conditions. They now live in a new ecosystem which has been shaped by humans. This means that restoring natural ecological systems can be a difficult objective, if possible" concludes Lluis Cardona.
Source: Universidad de Barcelona [January 19, 2017]